A prospective investigation to evaluate risk factors for lower extremity injury risk in male youth soccer players.

There is an inherent risk of injury in male youth football; however, pertinent risk factors for injury have yet to be examined. This study used a prospective cohort design with 357 elite male youth football players (aged 10-18 years) assessed during the preseason period and then monitored during the season recording all non-contact lower extremity injuries. Screening tests included single leg hop for distance (SLHD); 75% of maximum hop and stick (75%Hop); single leg countermovement jump (SLCMJ); and the tuck jump assessment (TJ). Players were divided into subgroups based on chronological age. SLCMJ peak landing vertical ground reaction force (pVGRF) asymmetry was the most prominent risk factor (U11-U12s, OR 0.90, P = .04; and U15-U16s, OR 0.91, P < .001). Maturational offset (OR 0.58, P = .04), lower right leg SLCMJ pVGRF relative to body weight (OR 0.36, P = .03), and advanced chronological age (OR 3.62, P = .04) were also significantly associated with heightened injury risk in the U13-U14s, U15-U16s, and U18s, respectively. Univariate analyses showed combinations of anthropometric and movement screening risk factors were associated with heightened risk of lower extremity injury; however, there was variability across the different chronological age groups. Greater SLCMJ pVGRF asymmetry, lower right leg SLCMJ pVGRF %BW, later maturation, and advanced chronological age are potential risk factors for injury in elite male youth football players, although the strength of these relationships was often low to moderate. In addition, risk factors are likely to change at different stages of development.

Sex differences in force attenuation: a clinical assessment of single-leg hop performance on a portable force plate.

OBJECTIVE: Impaired biomechanics and neuromuscular control have been suggested as probable links to female sex bias in the onset of patellofemoral pain syndrome. There are limited objective, clinical measures for assessment of impaired biomechanics and neuromuscular control. The primary objective of this investigation was to examine sex differences in vertical ground reaction force (vGRF) and force loading rate in young athletes performing maximum, repeated vertical single-leg hops (RVSHs). The authors hypothesised that females would demonstrate greater vGRF and force loading rate than males and show interlimb differences in force attenuation. DESIGN: Cross-sectional study. SETTING: Paediatric sports medicine clinic. PARTICIPANTS: 109 Healthy high school, soccer and basketball athletes. ASSESSMENT OF RISK FACTORS: Participants performed RVSHs for 15 seconds on a portable force plate with a sampling rate of 400 Hz (Accupower; AMTI, Watertown, Massachusetts, USA). MAIN OUTCOME MEASUREMENTS: Raw vGRF was filtered with a generalised cross-validation spline using a 50-Hz cutoff frequency and then normalised to potential energy. Force loading rate was calculated by dividing normalised vGRF by time-to-peak force. Group means were compared using analysis of variance. RESULTS: The females demonstrated significantly greater normalised vGRF (p<0.001) and force loading rate (p<0.001) during landing than their male counterparts. Neither sex demonstrated significant interlimb differences in force attenuation (p>0.05). CONCLUSIONS: The female athletes may have altered force attenuation capability during RVSHs as identified by increased vGRF and force loading rate compared with the male athletes. Portable force plates may be potential tools to identify altered force attenuation in clinical settings.

Resistance training among young athletes: safety, efficacy and injury prevention effects.

A literature review was employed to evaluate the current epidemiology of injury related to the safety and efficacy of youth resistance training. Several case study reports and retrospective questionnaires regarding resistance exercise and the competitive sports of weightlifting and powerlifting reveal that injuries have occurred in young lifters, although a majority can be classified as accidental. Lack of qualified instruction that underlies poor exercise technique and inappropriate training loads could explain, at least partly, some of the reported injuries. Current research indicates that resistance training can be a safe, effective and worthwhile activity for children and adolescents provided that qualified professionals supervise all training sessions and provide age-appropriate instruction on proper lifting procedures and safe training guidelines. Regular participation in a multifaceted resistance training programme that begins during the preseason and includes instruction on movement biomechanics may reduce the risk of sports-related injuries in young athletes. Strategies for enhancing the safety of youth resistance training are discussed.

Multiple risk factors related to familial predisposition to anterior cruciate ligament injury: fraternal twin sisters with anterior cruciate ligament ruptures.

OBJECTIVE: A multifactorial combination of predictors may increase anterior cruciate ligament (ACL) injury risk in athletes. The objective of this twin study was to examine these risk factors to identify commonalities in risk factors that predisposed female fraternal twins to ACL injury. METHODS: Female twins in high-risk sports were prospectively measured prior to an injury for neuromuscular control using three-dimensional motion analysis during landing, hamstrings and quadriceps muscular strength on a dynamometer and joint laxity using a modified Beighton-Horan index and a Compu-KT arthrometer. Intraoperative measures of femoral intercondylar notch width were recorded during ACL reconstruction. RESULTS: Abduction angles were increased at one knee in both of the twin sister athletes relative to uninjured controls at initial contact and at maximum displacement during landing. The twin female athletes that went on to ACL injury also demonstrated decreased peak knee flexion motion at both knees than uninjured females during landing. The twin athletes also had increased joint laxity and decreased hamstrings to quadriceps (H/Q) torque ratios compared to controls. Femoral intercondylar notch widths were also below the control mean in the twin siblings. CONCLUSIONS: Prescreened mature female twins that subsequently experienced ACL injury demonstrated multiple potential risk factors including: increased knee abduction angles, decreased knee flexion angles, increased general joint laxity, decreased H/Q ratios and femoral intercondylar notch width.

Serial assessments to determine normalization of gait following anterior cruciate ligament reconstruction.

There is an increased emphasis to identify clinically applicable methods that quantify gait deficits following anterior cruciate ligament reconstruction (ACLR). The purpose of this study was to perform serial gait assessments in a clinical setting to determine whether and when clinical gait parameters normalize in patients following ACLR. The hypothesis was that a clinically available gait treadmill would quantify gait deficits measured at 4 weeks post-reconstruction. The secondary hypothesis was that patients would demonstrate incremental improvements in these gait parameters measured at each interval up to 12 weeks post-reconstruction, and that the objectively measured improvements would correlate to the patient's subjective rating of function. Fifteen subjects, five male and 10 female, who had initial unilateral anterior cruciate ligament injury were selected for this study on the basis of operative data. All subjects were evaluated in a physical therapy clinic within 3 days following ACLR and were enrolled in a standardized rehabilitation program. The dependent gait variables of step length, stance time and gait velocity were measured at 4, 6, 8 and 12 weeks post-ACLR on a commercially available gait treadmill. A 2 x 4 multivariate analysis of variance (2 within factors) with measures for limb involvement (uninvolved and involved) and repeated measures for time (4, 6, 8 and 12 weeks) was used to assess the interactions and the main effects on the gait variables of stance time and step length. The results of this study supported the hypothesis that gait deficits and serial improvements can be objectively quantified in a clinical setting (P<0.001). Specifically, stance time, step length and gait velocity deficits evaluated at 4 weeks showed significant improvements at the measured intervals. Step length normalized at week 8. Stance time and gait velocity reached normal levels at the 12-week time interval. Subjective activity of daily living scores (ADLS) also improved following the 12-week rehabilitation, from 53+/-17% to a mean score of 88+/-11% (P<0.001). ADLS scores significantly correlated to step length (R=0.63) and stance time (R=0.53) in the involved limb. Self-selected gait velocity also correlated to ADLS scores and significantly predicted 49% of the variance in the subjective outcome measure. A clinically available gait treadmill can be used to quantify gait deficits and improvements following ACLR. Serial assessments of walking gait may aid clinicians to identify and target deficits in their patients during rehabilitation.

A pilot study to determine the effect of trunk and hip focused neuromuscular training on hip and knee isokinetic strength.

OBJECTIVE: The objective was to determine the effect of trunk focused neuromuscular training (TNMT) on hip and knee strength. The hypothesis was that TNMT would increase standing isokinetic hip abduction, but not knee flexion/extension, strength. METHODS: 21 high-school female volleyball players (14 TMNT, mean age 15.4 (1.4) years, weight 170.5 (5.0) cm, height 64.1 (8.5) kg and 7 controls, mean age 16.0 (1.7) years, height 173.4 (10.0) cm, weight 63.9 (5.3) kg; p>0.05) were recruited to participate in this study. The 14 TNMT subjects participated in a TNMT protocol (twice weekly) over a 10 week period in addition to their standard once-weekly off-season strength training. Standing isokinetic hip abduction strength and seated knee flexion/extension strength were measured before and after TNMT. RESULTS: A significant interaction of group and time was observed. The TNMT group increased isokinetic hip abduction strength approximately 15% (13.5% in the dominant leg: mean (SD) 46.6 (10.1) to 52.9 (11.4) foot-pounds and 17.1% in the non-dominant leg: 46.1 (10.4) to 54.0 (10.7) foot-pounds; p = 0.01). There was no difference in the control group in pre-test versus post-test measures. Post-test results also indicated no effect of TNMT on isokinetic knee extension (p = 0.57) or knee flexion (p = 0.57) strength. CONCLUSIONS: Ten weeks of TNMT increased standing hip abduction strength in female athletes. Increased hip abduction strength and recruitment may improve the ability of female athletes to increase control of lower limb alignment and decrease knee loads resulting from increased trunk displacement during sports activities.

The effects of age and skill level on knee musculature co-contraction during functional activities: a systematic review.

OBJECTIVES: To systematically review the current literature that relates the effects of age and skill level to motor control patterns of knee musculature co-contraction during functional movements. METHODS: A search of electronic databases was performed with the search terms specifying co-contraction (cocontract*, co-contract*, coactive* or co-activ*). The search was focused on the effects age and/or skill level and were limited by the keywords of age or skill level (skill*) or experience (experi*). RESULTS: The search yielded a total of six peer-reviewed manuscripts that met the search criteria and were included in the review. CONCLUSIONS: The relationship between adequate dynamic joint stability and efficient movement patterns are complex. Co-contraction related to age and skill development varies among studies due to technical and practical considerations. Adequate antagonistic co-contraction of hamstring musculature seems to be a component of all functional movements, possibly maintain dynamic knee stability and protect against excessive joint loads. Future investigations that further delineate the appropriate lower extremity agonist and antagonist relationships during dynamic tasks may help elucidate injury risk mechanisms in specific populations.

A review of electromyographic activation levels, timing differences, and increased anterior cruciate ligament injury incidence in female athletes.

Deficits in dynamic neuromuscular control of the knee may contribute to the higher incidence of anterior cruciate ligament (ACL) injury in female athletes. There is evidence that neuromuscular training alters muscle firing patterns, as it decreases landing forces, improves balance, and reduces ACL injury incidence in female athletes. The purpose of this review is to summarise the evidence for altered muscular activation and timing relative to ACL injury risk in female athletes.

Evaluation of a two dimensional analysis method as a screening and evaluation tool for anterior cruciate ligament injury.

BACKGROUND: Increased knee valgus predicts the risk of anterior cruciate ligament (ACL) injury, particularly in women. Reducing injury rates thus relies on detecting and continually evaluating people with relatively large valgus motions. OBJECTIVES: To examine the potential of a two dimensional (2D) video analysis method for screening for excessive valgus. METHODS: Ten female and 10 male National Collegiate Athletic Association basketball players had three dimensional (3D) knee valgus and two dimensional (2D) frontal plane knee angle quantified during side step, side jump, and shuttle run tasks. 3D valgus was quantified from external marker coordinates using standard techniques, and 2D data were obtained from both the frontal plane projections of these coordinates (2D-Mot) and manual digitization of digital video footage (2D-Cam). A root mean square (RMS) error was calculated between 2D-Mot and 2D-Cam data to evaluate the reliability of the latter. Correlations between 2D-Cam and 3D data (intersubject and intrasubject) were also conducted, and regression slope and r2 values obtained. RESULTS: 2D-Cam and 2D-Mot data were consistent for side step (RMS = 1.7 degrees) and side jump (RMS = 1.5 degrees) movements. Between subjects, 2D-Cam and 3D data correlated well for the side step (r2 = 0.58) and side jump (r2 = 0.64). Within subjects, 2D-Cam and 3D data correlated moderately for the side step (r2 = 0.25 (0.19)) and side jump (r2 = 0.36 (0.27)). CONCLUSIONS: The 2D-Cam method can be used to screen for excessive valgus in elite basketball players, particularly for movements occurring primarily in the frontal plane. This method may also be a useful training evaluation tool when large reductions in dynamic valgus motions are required.

Prevention of anterior cruciate ligament injuries.

Numerous studies have found that female athletes who participate in jumping and pivoting sports are four to six times more likely to sustain a knee ligament injury, such as anterior cruciate ligament (ACL) injury, than male athletes participating in the same sports [1-8]. A widening gender gap in the number of serious knee ligament injuries exists due to geometric growth in female athletic participation, coupled with the four- to sixfold higher injury rate. More than 50,000 serious knee injuries are projected to occur in female varsity intercollegiate and high school athletics each year [9, 10]. Most ACL injuries occur by noncontact mechanisms, often during landing from a jump or making a lateral pivot while running [2, 11]. Knee instability, due to ligament dominance (decreased medial-lateral neuromuscular control of the joint), quadriceps dominance (increased quadriceps recruitment and decreased hamstring recruitment and strength), and leg dominance (side-to-side differences in strength, flexibility, and coordination) are possible contributing factors to the increased incidence of knee injury in female athletes [5, 6]. In this review, dynamic neuromuscular analysis (DNA) training is defined, and a rationale is presented for correcting the neuromuscular imbalances that may result in dynamic knee instability during sports play. Dynamic neuromuscular training has been shown to increase knee stability and decrease knee injury rates in female athletes [5, 12.., 13.]. Preliminary research on athlete screening and injury prediction based on the three aforementioned imbalances also is presented with recommendations for developing screening protocols for the identification of high-risk athletes.